In order to achieve acceptable performance, most battery packs require frequent conditioning cycles and/or an active battery management system. Conditioning cycles bring the pack slowly up to full charge which attempts to equalize the state of the batteries in the pack. To equalize batteries means to reduce the gap between the weakest and strongest cell. Active battery management addresses this issue by providing a small localized charge or discharge across individual cells. Active battery management keeps the strongest and weakest cells closer to the average cell. This results in better pack performance but still well under the performance of an individual cell. Conditioning cycles are still required, but not as often as a pack without a battery management system.
A typical battery management system uses transistors in series with each cell to locally control the charge or discharge of the cell. Such systems typically dissipate extra power, limit pack capacity, and add expense to pack design and production. This is especially true for large, high power battery packs.
Typical portable power packs suffer from low power densities resulting in either low capacity packs or large packs with limited portability. Low power density thus limits the use of conveniently portable power packs in industrial power applications.
What is needed are circuits and methods to combine battery cells in high power portable battery packs or power supply systems to improve capacity, charge and discharge rates, lifespan, and other performance characteristics.